Mass storage and server systems continue to provide increased compute capacities to satisfy user demands. Photo and movie storage, and photo and movie sharing are examples of applications that fuel the growth in demand for larger, faster, and more reliable storage systems.
Part of a solution to these increasing demands is the use of arrays of multiple inexpensive disks. These arrays may be configured in ways that provide redundancy and error recovery without any loss of data. These arrays may also be configured to increase read and write performance. This may be accomplished by allowing data to be read or written simultaneously to multiple disk drives. These arrays may also be configured to allow “hot-swapping” which allows a failed disk to be replaced without interrupting the storage services of the array. Whether or not any redundancy is provided, these arrays are commonly referred to as redundant arrays of independent disks (or more commonly by the acronym RAID). The 1987 publication by David A. Patterson, et al., from the University of California at Berkeley titled “A Case for Redundant Arrays of Inexpensive Disks (RAID)” discusses the fundamental concepts and levels of RAID technology.
RAID storage systems may be connected to a host server system using multiple connections. These multiple connections provide redundancy which can ensure a high level of reliability. The multiple connections may also provide fast access and data transfer between the RAID system and the host server. Software in the server may be configured so that the storage array appears as one or more disk drives (or volumes). This is accomplished in spite of the fact that the data (or redundant data) for a particular volume may be spread across multiple disk drives or RAID systems.